In recent years, as computers have developed and become popular, various kinds of information are put into digital data. As a device for storing such digital data, there is a storage device such as a magnetic tape and a magnetic disk. Because data to be stored has increased day by day and the amount thereof has become huge, a high-capacity storage system is required. Moreover, it is required to keep reliability while reducing the cost for storage devices. In addition, it is required that data can be retrieved later with ease. As a result, such a storage system is desired that is capable of automatically realizing increase of the storage capacity and performance thereof, that eliminates a duplicate of storage to reduce the cost for storage, and that has high redundancy.
Under such circumstances, in recent years, a content address storage system has been developed as shown in Patent Document 1. This content address storage system distributes and stores data into a plurality of storage devices, and specifies a storing position in which the data is stored based on a unique content address specified depending on the content of the data.
To be specific, the content address storage system divides predetermined data into a plurality of fragments, adds a fragment as redundant data thereto, and stores these fragments into a plurality of storage devices, respectively. Later, by designating a content address, it is possible to retrieve data, that is, a fragment stored in a storing position specified by the content address and restore the predetermined data before being divided from the plurality of fragments.
Further, the content address is generated so as to be unique depending on the content of data. Therefore, in the case of duplicated data, it is possible to refer to data in the same storing positions to thereby acquire data of the same content. Accordingly, it is not necessary to separately store duplicated data, and it is possible to eliminate duplicated recording and reduce the amount of data.
[Patent Document 1] Japanese Unexamined Patent Application Publication No. JP-A 2005-235171
In a content address storage system, a content address specifying a storing position of stored data is stored as metadata, and specifically, metadata are hierarchically stored as the number of data increases. For example, FIG. 1 shows an example of metadata in the content address storage system. As shown in this drawing, metadata 181, 182 and 171 are composed of key parts 181a, 182a and 171a storing information representing positions of division data in an original file, and address parts 181b, 182b and 171b storing information representing storing positions of the data or other metadata. In a case that the address parts 181b, 182b and 171b store the same content addresses, these address parts refer to data in the same storing position.
However, in the content address storage system described above, for example, as shown by reference numerals 181b and 182b in FIG. 1, data of the same content may be stored in address parts within metadata. That is to say, a problem that content address data may be duplicated and recorded frequently and the amount of data increases arises.